UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.84 Safari/537.36

Steps to reproduce the problem:
1. Launch Chrome in incognito mode:
          'chrome-versions/chrome-win32-65.0.3311.0/chrome.exe',
          '--remote-debugging-port=9222',
          '--incognito',
          '--user-data-dir=C:\\Users\\Corion\\AppData\\Local\\Temp\\GUfaccVLWY',

          '--no-first-run',
          '--disable-gpu',
          'about:blank'
2. observe that the Window gets the "incognito mode" decorations
3. Connect to this process using the DevTools API, opening a new tab:
2018/01/05 23:03:07 Created new tab $VAR1 = {
          'devtoolsFrontendUrl' => '/devtools/inspector.html?ws=127.0.0.1:9222/d
evtools/page/92B4C27257C09FF3984203C6679421FF',
          'description' => '',
          'id' => '92B4C27257C09FF3984203C6679421FF',
          'url' => 'about:blank',
          'title' => '',
          'webSocketDebuggerUrl' => 'ws://127.0.0.1:9222/devtools/page/92B4C2725
7C09FF3984203C6679421FF',
          'type' => 'page'
        };
4. Watch a new window open that is not in incognito mode

What is the expected behavior?
No new window opens but a new tab in the incognito mode browser window

What went wrong?
The new tab is opened in a named window instead of an incognito window

Did this work before? No 

Chrome version: 63.0.3239.84  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: 

This behaviour is consistent since Chrome 59, which is the earliest version I test headless mode with.

A workaround is to use a temporary profile directory every time, but first-class support for incognito mode would be more welcome from the API.

Additionally, it would be great if the DevTools had a way to determine whether the browser is in incognito mode or not.